Method of rust-proofing concrete reinforcing elements



United States Patent METHOD OF RUST-PROOFIN G CONCRETE REINFORCIN GELEMENTS Leo Torstenv Ulfstedt, Sodertalje, Sweden, assignor, by mesneassignments, to Casius Corporation Limited, Montreal, Quebec, Canada NoDrawing. Application May 14, 1953 Serial No. 355,173.

Claims'priority, application Sweden'March'l3,,1953* 4 Claims. (C1.25-154) This invention relates to a method of rust-proofing iron andsteel. reinforcing elements intendedv to be. cast into concrete orsimilar structures.

For this purpose, methods of providing reinforcing elements with acoating. of a mineral composition, for example by treating the elements.with. acement-containing grout, silicate-containing.solutionsor thelike,are already known. Such. coatings. may be very-efiective, but they donot give..an..absolute. protection againstrust, since they function onlyby preventing, more or less, owingto their tightness, the admission. ofoxygen to the reinforcing elements, thus retardingrust-formation.

In order to improve the rust-preventing. effect ofsuch mineral coatings,it has been proposed to adinix to the coating compositibnpot'assiumchromate or other soluble chromates, in the presence of which ironcannot rust, due to the passivating effect of'thechromates ions on theiron. The use. of suchchromates has. two. drawbacks, however. Firstly,from the sanitary point of. view the use of chromate solutions suffersfrom the disadvantage that the workers handling the solutions oftencontract very troublesome allergic'diseases. Secondly, it is uncertainwhether the soluble chromate remains in the rust-protective coating fora sufficient time, as it is easily spread and dis t'ribut'ed in theconcrete owing to the wandering of moisture in the reinforced concretestructure, so that the. concentration of chromate ions around the. ironsmaysoon be insuflicient to produce. the intended effect.

According to thepresent invention the drawbacks and inconveniencesindicated above are eliminated by adding the chromate in the form of theextremely ditlicultly soluble barium chromate;

The invention is basedzonsthe factsfthatibarium sulfate is still less:soluble. than barium: chromate, while alkali metall chromates as"v wellas: calcium chromate. are easily soluble, and further" that: the:hydraulic and other. masses,

into which reinforcing: elementsare generally embedded, generallycontain sulfates, or without any inconvenience may be mixed: with a.small quantity of sulfates, whereby a successive conversion of thebarium chromate with formation of barium sulfate. and an easily'soluble.chroit will not contain chromate. ions; in concentrations dan-- gerousto health. When the elements after. the' application of' thecoating'thereonand. drying the; coating. have been cast intosulfate-containing concrete, or sulfate-containing masses of similarkind, the water. present in the mass (concrete), which always containssmall amounts of sulfate dissolved: therein, penetrates. into therust-protective coating, whereby the barium chromate contained'in thecoating reacts extremelyslowly with the'sulfate. This 1 resultsinth'eprecipitation of barium-sulfate and the formation ofa-sol'ublechroma'te, whereby" the chromaterom concentration'risestovalues sufficient to secure a passivat-ion of the reinforcing irons. Ifthe cast mass, when set, is allowed or caused. to dry completely,obviously this conversion is discontinued, but at the same time alsothemain cause of rust-formation is eliminated, no moisture being present.If the. concrete. should later absorb moisture, sulfate is again capableof diffusing onto the barium chromate. in thecoating on the irons,whereby thechromate. ion-concentration requiredfor passivating theironsis again restored.

Y The content of sulfate required in. the mass into which the.reinforcing elements provided with a barium chromate-containing coatingaccording to theinvention are. to be cast,.-need not be great. It has.been found in the case of commoncement concrete, the binder of which isPortland cement. containing sulfate corresponding to 1-3% 1 to add tothecoating compositionmay vary within comparatively wide limits. In viewof the fact that even very low chromate ion-concentrations aresufiicient; to produce the desired passivating. effect. of the.reinforcement irons,

. and sincethe relatively small difference in the solubility of the.barium. chromate and the. barium, sulfate results in a very slowformation of. chromateions, evena comparatively low content. ofbariumtchromate in the. coating issufficient to secure the maintenanceof the required chromate ion-concentration in the neighbourhood of thereinforcing elements for a very long period of time. Further, as alreadyindicated above, when the cast concrete has set and its moisture contenthas decreased, the possibilities of the diffusion of sulfate ions aswell as chromate ions are reduced, which results simultaneously in aretarded production and a-retarded removal of chromate ions.

With regard to the above-mentioned facts, even. a barium-chromatecontent of. about 1%, based on the solid components in the coatingcomposition, is often sufficient and suitable for obtaining the desiredeffect. However, in certain cases it may be preferable to. add the.barium chromate in a considerably higher concentration, especially inthe case of'concrete structures which are exposed to the stronginfluence of moisture over long periods. Thus the barium chromatecontent in such cases may amount I05, 1 0, 20 or even 40-50% of theother solid components in the coating composition.

Apart from thecontent of barium chromate, the coatingcompositionaccording to theinvention may be composed in any suitable manner, forexample as disclosed and claimed in. my and Simonssons joint prior US.

.coating remains reactive with water and unites with concrete in whichthe coated reinforcing elements. are subsequently embedded, as describedin the above-mentioned patents; As examples of such binding agents maylulose.

forming calcium silicates, as described in the Patent No. 2,611,945.

As is well-known, common, dense cement concrete constitutes in itself acomparatively effective rust-protection for the reinforcing ironsembedded therein. However, this is not the case with light-weightconcrete, and for this'reason the application of the invention has itsgreatest importance in connection with concrete of the latter kind. 'Bylight-weight concrete according to the application is to be understoodconcrete which has been produced from light aggregate together with theusual binders, as well as concrete which has been manufactured byproducing pores in the concrete mass by the addition of gas-developingof foam-producing agents, independently of whether the light-weightconcrete thus produced is then left to set under the influence ofmoisture and air,

or steam-cured by means of pressure-steam, for example at anover-pressure of 8-12 kgs. In the latter case, the

application of the invention has been found to be especially favourable,in so far as it has proved thatthe sulfate-content in steam-curedconcrete is generally present in a very easily soluble form.

When carrying out the invention in practice, the mineral coatingcomposition containing barium chromate is first prepared by mixing thecomponents together to a homogenous liquid, preferably aqueoussuspension. The iron or steel reinforcing elements are then coated withthe resulting grout or slurry in any suitable manner, for example bydipping, brushing, spraying or other methods. The coating thus appliedis thereupon dried by exposing it to the air or, if it is desired toaccelerate the drying, to a current of heated air of a temperature ofabout C., for example.

The so-coated reinforcing elements are embedded in concrete,light-weight concrete or like masses and the coating is united with theconcrete during setting or steam-curing and forms, when the concrete hasfinally set and hardened, an effective bond between the reinforcingelements and the concrete at the same time serving as an effectiverust-protective for the elements, due to, the presence of barium chomatetherein, as indicated above.

In the following specific non-limitative examples the application of theinvention is described more in detail. The parts in the examples areparts by weight.

and iron or steel reinforcing elements are dipped therein. After dryingof the coating the elements are cast into common concrete, consisting ofPortland cement, sand, gravel and water.

Example 2 Iron or steel reinforcing rods are treated with a mixture ofParts Water-glass solution (common market product) 100 Barium chromate50 When the coating has been dried, the rodsare cast into 4 afoam-concrete prepared from slag cement, fine sand, water and a foamingagent.

Exainple 3 A mixture is prepared from Parts Portland cement 100 Bariumchromate 20 Casein 6 Water 42 and iron or steel reinforcing elements aredipped therein. When the coating has dried, the elements are cast into alight-weight concrete prepared from Portland cement, groundquartz-containing sand, water and aluminum powder, which light-weightconcrete after setting is steamcured in autoclave at an over-pressure of10 kgs. per

sq. cm.

Example 4 Iron or steel reinforcing elements are coated with a mixtureconsisting of Parts Finely ground quartz-containing sand 100 Slaked lime25 Barium chromate 10 .A water-soluble cellulose ether 3 Water 50 Afterthe coating has been dried, the elements are cast into a light-weightconcrete mixture consisting of ground, unslaked lime, fly-ash, water andaluminium powder, and

- if desired, 1% gypsum, in a mold. After setting the reinforcedconcrete bodies are steam-cured 1n autoclave with steam at anover-pressure of 8 kgs.

Example 5 Iron or steam-reinforcing elements are treated with a mixtureprepared from When the coating has been dried, the elements are castinto a light-weight concrete prepared from cement, granulated blastfurnace slag and water, in a mold, whereupon the setting and hardeningof the concrete bodies thus produced is accelerated by exposing thebodies to a moisture-saturated atmosphere at C.

What I claim is:

1. In the making of reinforced concrete and similar structures, whereinrust-proofed steel and iron reinforcing elements are embedded inconcrete and similar masses containing small amounts of water-solublesulfates, the process which comprises coating the reinforcing elementswith a liquid grout of a mineral composition containing at least about1% barium chromate, based on the weight of the solid components of thecoating composition and about 2-20% of a hydrophilic organic colloidalbinding material which at least swells in water, drying the coatingbefore setting takes place, and surrounding the reinforcing elementswith an aqueous slurry of the concrete composition, whereby the coatingon the reinforcing elements sets and unites with the concrete duringsetting thereof, producing effective joints between the reinforcingelements and the concrete, the said barium chromate being adapted toreact with the water-soluble sulfates when moisture is present in thesurrounding mass to form barium sulfate and chromate ions having apassivating effect on the iron.

2. In the making of reinforced concrete, wherein rustproofed steel andiron reinforcing elements are embedded in concrete containing smallamounts of water-soluble sulfates, the process which comprises coatingthe reinforcing elements with a liquid aqueous grout of Portland cementcontaining at least about 1% barium chromate, based on the weight of thesolid components of the coating composition, and a small proportion ofcasein sufiicient to render the coating tough and to produce a bindingaction in the coating, drying the coating before it has had time to set,and embedding the so-coated reinforcing elements in a slurry of ahydraulic cement and steamcuring the cement, whereby a reinforcedconcrete is produced with effective joints between the reinforcingelements and the concrete, the said barium chromate being adapted toreact with the water-soluble sulfates when moisture is present in thesurrounding mass to form barium sulfate and chromate ions having apassivating effect on the iron.

3. In the making of reinforced steam-cured 1ight-weight concrete,wherein rust-proofed steel and iron reinforcing elements are embedded inconcrete containing small amounts of water-soluble sulfates, the processwhich comprises coating the reinforcing elements with a liquid aqueousgrout of Portland cement containing at least about 1% barium chromate,based on the weight of the solid components in the coating composition,and a small proportion of a hydrophilic organic colloidal bindingmaterial sufficient to render the coating tough and to produce a bindingaction in the coating, drying the coating before it has had time to set,and embedding the so-coated reinforcing elements in a slurry of Portlandcement containing a gas-producing agent in an amount suflicient toproduce a porous concrete, and subjecting the whole to a curing bypressure-steam, whereby a reinforced porous steam-cured light-weightconcrete is pro duced with effective joints between the reinforcingelements and the concrete, the said barium chromate being adapted toreact with the water-soluble sulfates when moisture is present in thesurrounding mass to form barium sulfate and chromate ions having apassivating effect on the iron.

4. The process of claim 3 wherein the liquid aqueous grout comprisesapproximately the following: parts of Portland cement, 20 parts bariumchromate, 6 parts casein, and 42 parts water, and the embedding slurrycomprises approximately the following: Portland cement, groundquartz-containing sand, aluminum powder and water, and wherein thecoated reinforcing elements and slurry, after setting, are steam curedat a pressure of 10 kgs. per sq. cm.

References Cited in the file of this patent UNITED STATES PATENTS 96,936Mariner et a1 Nov. 16, 1869 2,105,324 Huttemann et a1 Ian. 11, 19382,374,562 Owens Apr. 24, 1945 2,416,064 Patterson et a1 Feb. 18, 19472,430,589 Sloan Nov. 11, 1947 2,591,625 Simonsson Apr. 1, 1952 2,611,945Simonsson Sept. 30, 1952 2,668,122 Pitrot Feb. 2, 1954

